osd: fix automatic prepare when auto_discover
osd: fix automatic prepare when auto_discover

Use `devices` variable instead of `ansible_devices`, otherwise it means
we are not using the devices which have been 'auto discovered'

Signed-off-by: Guillaume Abrioux <30a9df5a0293a6108675377fa1673f7aa713f915@redhat.com>
(cherry picked from commit d5dfc63c89268c51253f3465a6e39be7cdfe12e4)

fgal/ceph-ansible,fgal/ceph-ansible